An aircraft piston engine is a main power plant of a general aviation aircraft. Frictional wear of a cylinder-piston assembly is one of main mechanical faults of an aircraft engine system. As shown in FIG. 1, the cylinder-piston assembly includes a cylinder assembly 11, a piston 12 and a connecting 13. The cylinder assembly 11 includes a cylinder barrel 111 and a cylinder head 112. Part of the cylinder barrel 111 extends into the cylinder head and is matched with the cylinder head 112. The cylinder barrel 111 is formed by forging high-strength steel alloy with high price. An integral radiating fin is arranged in the middle, and an inner surface is nitrogenized and precisely honed into specific flat-top mesh. The cylinder head 112 is formed by casting aluminum alloy, has the characteristics of good thermal conductivity, light weight and the like, can remarkably reduce the integral weight of the engine, and structurally includes an air inlet rocker arm, an air outlet rocker arm, a spark plug, an air inlet valve 1121, an air outlet valve 1122, a radiating fin and the like. Therefore, the cylinder assembly 11 has high technical complexity and high value-added, and has important maintenance and remanufacturing values.
The aircraft piston engine is always under harsh working conditions of intermittent operation (long-term parking and occasional flight), full-power operation (takeoff, creeping, full-speed flight and other phases) and instable cooling (a cooling effect is relevant to advancing speed of the aircraft), especially, a position of a stop point on the cylinder-piston assembly often forms a semi-dry friction or dry friction state due to high-temperature combustion of lubricating oil. In addition, gas pressure, speed and direction of a movement of a piston 12 are in changed rapidly. Therefore, the cylinder and a piston ring are prone to wear, scratch and even fracture, and the mesh on the inner surface of the cylinder barrel 111 is prone to wear. The wear failure of the cylinder-piston assembly occupies 45%-65% of the frictional wear fault of the aircraft piston engine, and also directly causes short overhaul time interval and service life of the aircraft piston engine.
Since assembly and disassembly of the cylinder barrel 111 and the cylinder head 112 of the aircraft piston engine need a special necking-bulging technology. If a waste cylinder assembly 11 is disassembled in an overhaul process, this process has lost remanufacturing value and significance from the perspective of reliability and economy. Therefore, in the case where the cylinder barrel 111 is not disassembled, a hole in the cylinder barrel 111 is a blind hole 1111.
At present, for deep maintenance of the waste cylinder assembly 11 of the aircraft piston engine, a foreign traditional “cylinder expansion+honing” maintenance mode still dominates. This maintenance mode not only requires high processing accuracy to satisfy a dimensional allowance standard, but also requires to select a larger nonstandard piston assembly, thereby causing interchangeability damage of parts, limited maintenance times and low utilization ratio of waste elements, and further causing high use and maintenance cost of the aircraft piston engine and great waste of value-added and also affecting the service life and flight safety of the general aviation aircraft and a military UAV.
Existing plasma spraying of an inner hole includes two modes. The first mode is as follows: a workpiece rotates (on a lower side), and a spray gun moves up and down (on an upper side) along a vertical direction. However, since a structure of the cylinder head 112 of the aircraft piston engine is complicated and not symmetrical (e.g., different numbers of radiating fins with different sizes are distributed around the cylinder head 112), a center of gravity of the cylinder assembly 11 is not in a center of the blind hole. The cylinder assembly 11 is not stably and is easy to being eccentric during high-speed rotation, thereby causing uneven mass and thickness of prepared coatings. Meanwhile, dust is easier to sink and accumulate in the blind hole with an upward opening, and is difficult to remove, thereby causing pollution to the coating and affecting coating quality. The other mode is as follows: the workpiece is fixed (on a lower side), and the spray gun rotates (on an upper side). The spray gun is positioned in a center of the inner hole, and a spraying distance is fixed and is smaller than a radius of the inner hole, but the inner diameter of the blind hole of the cylinder assembly 11 is small and a short spraying distance is not enough to melt the powder, thereby generating a large number of powder and inclusions in the coating and reducing coating quality. Meanwhile, short-distance spraying causes a rapid temperature rise of the cylinder assembly 11 and a great deformation.
Therefore, the existing plasma spraying modes of the inner hole are only suitable for material-adding repair of through holes, large holes and regular inner holes. For the waste cylinder assemblies 11 of the aircraft piston engine with precise and complicated structure, asymmetry, small aperture and high strength of blind hole and inner wall, high-quality remanufacturing for these waste cylinder assemblies 11 of the aircraft piston engine cannot be realized through an existing technical solution. Scratch, wear, corrosion and other failure manners generated on the inner wall of the cylinder barrel 111 currently cannot be effectively repaired, thereby causing low utilization ratio of waste elements, poor part interchangeability and reduced overall performance, generating a large number of scrapped cylinders and causing huge resource waste and economic loss.